Wisconsin ADU Laws

Complete 2026 guide to accessory dwelling unit regulations

○Local Control Only

📋Quick Facts

Max Size
900 sq ft
Owner Occupancy
May be required
Parking
Set locally
Approval Process
Varies locally

📜Recent Legislation

AB365 (2025) - Proposed statewide ADU mandate, would require political subdivisions to allow ADUs by right

AB449 (2025) - Companion ADU legislation

Madison zoning reforms (2024) - Eliminated owner-occupancy requirement, allowed ADUs on properties with up to 8 units

Madison ADU streamlining (2021) - Shortened approval process for ADUs

⚠️Key Requirements & Restrictions

  • •No statewide ADU law yet - legislation pending in 2025-2026 session
  • •Rules vary dramatically by municipality
  • •Madison: max 900 sqft, 2 bedrooms max, no owner-occupancy requirement (as of 2024)
  • •Some municipalities ban ADUs entirely
  • •Proposed AB365 would require by-right approval statewide

📖Detailed Analysis

No statewide ADU law yet but significant legislation pending. AB365 (2025) proposed by Rep. Francesca Hong and Sen. Kelda Roys would require political subdivisions to allow ADUs by right, prohibit unique restrictions/fees, and nullify HOA prohibitions. Madison is state ADU leader with progressive policies: eliminated owner-occupancy requirement (2024), allows ADUs on properties with up to 8 units, streamlined permitting (2021), max 900 sqft/2 bedrooms. Milwaukee also allows ADUs. However, construction remains limited - only 32 ADUs built in Madison since 2012 despite policy liberalization. Cost remains barrier ($200k-$300k for detached unit). League of Wisconsin Municipalities supports ADUs but opposes state mandates, preferring local control. If AB365 passes, Wisconsin would join states with comprehensive ADU reform. Strong bipartisan interest including conservative Wisconsin Institute for Law & Liberty support.

🔗Official Resources

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⚠️ Disclaimer

The information provided on this website is for general informational purposes only and does not constitute legal, financial, or professional advice. ADU laws, regulations, and requirements vary by jurisdiction and change frequently. While we strive to keep this information accurate and up-to-date, we make no representations or warranties of any kind about the completeness, accuracy, reliability, or suitability of this information. Always consult with qualified local professionals, including attorneys, architects, and your local planning department, before making any decisions regarding ADU construction or investment. Use of this information is at your own risk.

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Last updated: February 2026